Secondary emission amplifying tube circuit



Feb. 14, 1950 v w 2,497,640

SECONDARY EMISSION AMPLIFYING TUBE cmppn Filed July 20, 1946 VJNVENTOFKADELBEPC VAN WEEL BYZ4% %7 AGENT Patented Feb. 14, 1950 SECONDARYEMISSION AMPLIFYING TUBE CIRCUIT Adelbert van Weel, Eindhoven,Netherlands, as-

signor to Hartford National Bank and Trust Company, Hartford, Conn, astrustee Application July 20, 1946, Serial No. 685,202 In the NetherlandsAugust 23, 1943 Section 1, Public Law 690, August 8, 1946 Patent expiresAugust 23, 1963 2 Claims.

Thisinvention relates to a circuit-arrangement for the transmission ofelectric oscillations, particularly of a wide frequency band or ofultrahigh frequencies, in which a discharge tube is used which isprovided with a secondary emission electrode which also acts as anoutput electrode and which in the proximity of the secondary emissionelectrode andin the path of the secondary electrons comprises a gridwhose bias is higher than that of the secondary emission electrode.

It is known that in the so-called wide band amplifiers the width of thefrequency band to be transmitted is solely determined by the capacityoccurring between the output electrode and the cathode; the lower thesaid capacity, the larger is the frequencyband allowed to pass. Thisremark applies both to circuit-arrangements for the transmission ofmodulated oscillations (for example high or intermediate frequencyamplifiers for television or for frequency-modulated oscillations) andto circuit-arrangements for the transmission of non-modulatedoscillations (for example video frequency amplifiers for television). Inaddition, in amplifiers for ultra-high frequency oscillations themaximum impedance of the output resonant circuit and consequently theachievable amplification are also solely determined by the capacitybetween output electrode and cathode. It is therefore of paramountimportance to take care that this capacity is minimized incircuit-arrangements of the said descriptions.

In the transmission of wide frequency bands and of ultra-highfrequencies the amplification to be obtained is generally limited, sothat for this purpose use may be made with advantage of the so-calledsecondary emission tubes, which have a very high mutual conductance. Itmay, in some cases, be of use to employ the secondary emis-- sionelectrode also as an output electrode. This measure may be taken, forexample, if an amplification without phase shift is desired or if twofrequency bands (for example, image and sound frequencies in television)are to be separated; in the latter case the oscillations associated withone of the bands may be taken from the anode and the oscillationsassociated with the other band from the secondary-emission electrode.

Now, a grid is frequently arranged in secondary emission tubes in theproximity of the secondaryemission electrode and in the path of thesecondary electrons, said grid having a higher bias than thesecondary-emission electrode, for example the same bias as the anode,and having the function of drawing away thesecondary electrons from thesecondary-emission electrode. This grid is generally connected direct tothe anode inside the tube; its has, however, also been suggested beforeto provide the grid concerned with a separate supply lead. In the use ofsuch tubes in circuit-arrangements for thetransmission of a widefrequency band or of ultra-high frequencies, there is the disadvantagethat the capacity between the secondary emission electrode and thecathode is comparatively high, so that the secondary emission electrodecannot be utilized without difficulty as an output electrode.

The invention has for its object to obviate t'his disadvantage Accordingto the invention, to-this end a high impedance for the oscillations tobe transmitted is provided between the said? grid and the source ofdirect voltage which supplies the bias for this grid.

The said grid is preferably connected to the source of direct voltagethrough a high-ohmic resistance. For this purpose the said resistancemay be arranged, for example, inside the tube between the said grid andthe anode.

In order that the invention may be clearly understood and readilycarried into effect, it will now be explained more fully with referenceto the accompanying drawing, in which one form of construction isillustrated.

On the drawing is shown an amplifier for a wide frequency bandcomprising a discharge tube 1 which is provided with a cathode 2, acontrol grid 3, a screen grid 4, a secondary emission electrode 5, agrid 6 arranged in the path of the secondary electrons and an anode I.The oscillations to be amplified are supplied to the control grid 3through terminals 8 and 9. The circuit of the secondary emissionelectrode includes a resistance I 0, from which the amplifiedoscillations are obtained through terminals H and I2. The anode I isconnected to earth, via a condenser l3, for the frequencies of theoscillations to be amplified. A resistance l4 shunted by a condenser isincluded in the cathode lead in the usual manner for the generation ofthe control grid bias.

According to the invention, the grid 5 is connected to the anode 1through a high-ohmic resistance l5. The effect of this measure may beexplained as follows.

In the usual circuit-arrangements the grid 6 was connected direct to theanode l, the capacity between the secondary-emission electrode and earthbeing primarily constituted by the capacity C1 between thesecondary-emission electrode and the anode and by the capacity C2between the secondary-emission electrode and the grid 6 and beingconsequently Ci-l-Cz; the other capacities between thesecondary-emission electrode and earth (for example, the parasiticcapacity of the resistance l and the capacity between thesecondary-emission electrode and the screen grid 4) may be assumed to beincluded in the capacity C1.

In the circuit-arrangement according to the invention the grid 6 ispractically insulated with respect to earth by the high impedanceincluded in the circuit of this grid, so that for the capacity betweenthe secondary emission electrode and the grid 6 is substituted theseries combination of this capacity and the capacity 03 between the grid6 and the anode 1. Thus, the total capacity between thesecondary-emission electrode and earth is and is consequently lower thanin the usual circuit-arrangements. A considerable reduction (for exampleof several pis.) of the total output capacitive reactions is obtainablein practice by the use of the invention.

In order to avoid an increase of the output capacity by the capacity ofthe supply lead of the grid 6 with respect to the anode and thesecondary-emission electrode the resistance I is preferably arrangedinside the tube between the grid 6 and the anode. The resistance l5 may,in practice, have a value of several megohms. The invention may also beused with advantage in circuit-arrangements in which the tube l isprovided with a photo-electric cathode instead of the cathode 2 and thecontrol grid 3.

What I claim is:

1. An electric wave transmission circuit comprising a thermionicdischarge tube having a cathode, anode, secondary emissive electrode anda grid included in the electron path between said anode and secondaryelectrode, a source of desired signals, means to modulate the electronpath of the said thermionic discharge tube in accordance with saidsignals, a first source of direct current potential of given voltage, anoutput stage, means to couple said first source of potential and saidoutput stage to the secondary emissive electrode-cathode circuit of saidthermionic discharge tube, a resistive element, means to connect saidresistive element between said grid and the anode of the said thermionicdischarge tube, a second source of direct current potential having ahigher voltage than the first source of potential, and means to connectsaid second source of potential to the anode of said thermionicdischarge tube.

2. An electric wave transmission circuit comprising a thermionicdischarge tube having a cathode, anode, secondary emissive electrode anda grid included in the electron path between said anode and secondaryelectrode, a resistive element connected internally in said thermionicdischarge tube between the anode and the grid, a first source of directcurrent potential of given voltage, an output stage, means to couplesaid first source of potential and said output stage to the secondaryemissive electrode-cathode circuit of said thermionic discharge tube, asecond source of direct current potential having a higher voltage thanthe first source of potential, and means to connect said second sourceof potential to the anode of said thermionic discharge tube.

ADELBERT VAN WEEL.

REFERENCES CITED The following'references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,201,587 Krawinkel May 21, 19402,276,417 Preisach Mar. 17, 1942 2,298,960 McRae Oct. 13, 1942

